TALLADEGA, Ala. — Brad Keselowski refused to be knocked down — not by Matt Kenseth, who jumped him from behind after a disastrous race at Charlotte, and not by garage-wide condemnation over his post-race meltdown. He kept his head up and arrived at Talladega Superspeedway determined to shake off a bad week that earned him a $50,000 fine from NASCAR and moved him to the edge of elimination in the Chase for the Sprint Cup championship. Only a win would keep his title hopes alive.